For many articles, especially metal objects such as rolling-mill products, namely, structural shapes having webs and flanges, it is frequently necessary to determine the thickness of portions of the article, e.g. the web or flange, during the manufacturing process. When the manufacturing process involves the use of a rolling-mill line comprising a plurality of rolling stands interconnected by a conveyor, e.g. a roller conveyor, along which the article is displaced, the measuring device can be provided along this line for the nondestructive measurement of the thickness of a selected portion of the article utilizing, for example, a radiation source. While the present invention is concerned primarily with thickness measurement, it has general application to nondestructive testing utilizing radiation sources of the type described.
In gammametric measurements of the aforedescribed type, the radiation source may be rich in gamma emissions and, in general, a plurality of such sources is required, the sources being calibrated so that each has a respective gamma energy.
Gammametric apparatus of the aforedescribed type may be utilized to control the rolling process or to ascertain the corresponding dimension of the product, or even to determine whether the product corresponds to an appropriate standard.
While efforts have been made to use gammametric measurements for this purpose heretofore, they have been less than successful because of the dangers inherent in the use of gamma-ray sources.